Conventional beverage can bodies typically are produced in large quantities by a drawing and ironing process. Conventional beverage can ends are formed in a press and then attached to the can body by a double seam.
Internal pressure in beverage cans may subject the scores on the ends of these cans to high forces upon tab actuation and the subsequent formation of cracks in the scores. In some circumstances, high internal pressures can cause sudden, unsafe score rupture or panel failure (for example, missiling) upon opening.
To achieve safe venting in conventional pressurized beverage cans with openings that have an area that is less than a majority of the center panel (such as on conventional 12 ounce beverage cans), can makers typically employ a feature that pauses the propagation of a single score line that defines the perimeter of the opening. Single score lines for beverage cans usually have a check slot to pause score propagation. A check slot is a score residual (that is, the metal at the bottom of the score) that is thicker than other portions of the score. Because the score residual is thicker, the check slot inhibits propagation of the score rupture so that a portion of the internal pressure vents before the remainder of the score is ruptured. In this way, for conventional beverage ends, check slots slow or pause score propagation to provide adequate venting early in the opening process.
Beverage cans with openings that have areas greater than a majority of the center panel, such as full aperture ends, are also known. U.S. Pat. No. 7,922,025 (Heinicke) is directed to venting cans having internal pressure of 25 psi or above, as sometimes found in packaging for nuts and other food items, tennis balls, and the like. Similarly, United States Publication Nos. 2011/0056945A1 (“Ramsey”) and 2011/0303672A1 (“Fields”) disclose venting cans having internal pressure of greater than 70 psi. However, the structure taught in Heinicke is not suitable for very high pressure applications, such as soft drink cans. Further, the ends disclosed in Ramsey and Fields have not yet been widely commercially adopted. There is a need for improved robustness of soft drink cans, which typically have vent test ratings of at least 90 psi.
Conventional thinking for venting full aperture can ends has been to control, especially by temporarily inhibiting or slowing, score rupture propagation by features that mechanically arrest the score rupture, increasing score residual in food can ends, and the break line scores in Heinicke. The Ramsey and Fields applications contradicted this thinking by teaching that a vent score that does not have an arresting mechanism will rupture more quickly, such that an opening having sufficient area created by such a vent score releases high internal pressures in the can before those pressures have the opportunity to tear the can end. In this regard, the venting referred to in this application is venting internal beverage can pressure upon opening, as distinguished from a vent that is opened after internal pressure has been released and that has the purpose of improving pouring.